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Full text of "Practical Organic Chemistry"

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2. Hofmann Bottles. The substance, if liquid, is introduced
into a small stoppered glass bottle known as a Hofmann bottle
''see  Fig. 28).    The dry bottle with  the stopper  is  carefully
&" weighed  and  then filled with liquid through a tube
^      drawn out into a wide capillary.    The stopper is in-
serted and the bottle reweighed.   It should hold about
o'i gram of substance.
3. A narrow graduated tube holding  50 c.c. and
divided into tenths of a c.c.
^         4. A large crystallising dish which serves as a gas
FIG. 28.   trough.
5. A long and wide cylinder in which the graduated
tube can be submerged in water.
6. A Bunsen burner with chimney.
The apparatus is set up as shown in Fig. 27. The Victor
Meyer apparatus is thoroughly dried by blowing air through by
means of a long glass tube, which reaches to the bottom of the
bulb. A small quantity of clean dry sand previously heated in
a crucible or a pad of asbestos is placed at the bottom of the
bulb to break the fall of the Hofmann bottle, when it is dropped
in. The bulb of the outer jacket is filled two-thirds full of
water and the displacement apparatus is clamped within it, so
that it nearly touches the liquid. The apparatus and jacket
must be adjusted at such a height that the capillary side limb
dips under the water contained in the crystallising dish, placed
on the bench. The graduated tube is filled with water and
inverted under the water in the crystallising dish and clamped
there until required. The burner protected from draughts by
the chimney is lighted under the outer jacket and the displace-
ment apparatus left open at the top. To avoid inconvenience
arising from the steam, a split cork, into which a bent glass tube
is inserted, is pushed loosely into the open end of the jacket.
Whilst the water is boiling steadily and not too violently, the
substance is weighed. Chloroform, b.p. 61, or pure and dry
ether, b.p. 34-5 (see Prep. 3, p. 59), may be used for the
experiment, as their boiling-points lie well below that of water.
Before introducing the bottle and liquid, the apparatus must
be tested to ascertain if the temperature is constant. As
a rule \ hour's boiling suffices. Push in the rubber cork and
note if within the next minute or two any bubbles escape. If